At one point, I disciplined myself to write down or record some of the deep, philosophical thoughts I had while on mushrooms or acid or whatever. I stopped doing that because--once sober--I realized most of those "profound" thoughts were profoundly stupid and the kind of dumb shit someone tripping balls thinks is smart.
I've done that too. The difference between going back and reading nonsense and reading something insightful and creative is, in my experience, solely a function of how strong your writing and thinking skills are. If you are high, and feel you are having an incredible insight, you probably are. The ability to explain a brand new, mind-blowing insight is a massive undertaking of discipline: your mind is racing with new thoughts and exploring new ways to think about the world, and you have to put all of that on pause, digest it bit by bit, and explain something in writing that no one had been able to get through to you up to that point. Its not that 'muh altered state of mind makes me dumb,' its that you do not appreciate how difficult it is to communicate new ways of thinking.